Shock resistant fluid dynamic bearing motor

ABSTRACT

A system, method and means is provided for withstanding mechanical shock for use with fluid dynamic bearings. A sealing system is provided that withstands  1000  G shock events. In an aspect, a grooved pumping seal employed between a thrust plate and a shield, a thrust plate having spiral grooves, a fluid recirculation passageway, and a reservoir creates an asymmetric pressure gradient. In an aspect, fluid is retained and air is purged utilizing an enlarged fluid reservoir, axial channels and an angled fill hole. In an aspect, a shaft is attached to a top cover supplying radial stiffness, and an enlarged single-sided thrust plate improves dynamic parallelism.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from and benefit under 35 U.S.C. sec.120 as a Divisional patent application of co-pending U.S.non-provisional patent application Ser. No. 10/632,449, filed Jul. 31,2003, entitled “Method And System For Withstanding Shock In A SpindleMotor Bearing,” assigned to the assignee of the present application andincorporated herein by reference. In the above-referenced patentapplication Ser. No. 10/632,449, the method claims were classified bythe U.S. Patent and Trademark Office under class 29, subclass 893. Thisapplication is based on a provisional application Ser. 60/456,896, filedMar. 21, 2003, attorney docket STL 3333.01, entitled Top Cover AttachFDB With Inverted Sealing, and assigned to the Assignee of thisapplication and incorporated herein by reference.

FIELD

The invention relates generally to spindle motors, and more particularlyto a sealing system that withstands mechanical shock events for use withfluid dynamic bearings in disc drive data storage systems.

BACKGROUND

Disc drive memory systems are widely used throughout the world today.These systems are used by computers and devices including digitalcameras, digital video recorders, laser printers, photo copiers andpersonal music players. Disc drive memory systems store digitalinformation that is recorded on concentric tracks of a magnetic discmedium. Several discs are rotatably mounted on a spindle, and theinformation, which can be stored in the form of magnetic transitionswithin the discs, is accessed using read/write heads or transducers. Theread/write heads are located on a pivoting arm that moves radially overthe surface of the disc. The discs are rotated at high speeds duringoperation using an electric motor located inside a hub or below thediscs. Magnets on the hub interact with a stator to cause rotation ofthe hub relative to the shaft. One type of motor is known as an in-hubor in-spindle motor, which typically has a spindle mounted by means of abearing system to a motor shaft disposed in the center of the hub. Thebearings permit rotational movement between the shaft and the hub, whilemaintaining alignment of the spindle to the shaft. The read/write headsmust be accurately aligned with the storage tracks on the disc to ensurethe proper reading and writing of information.

Spindle motors have in the past used conventional ball bearings betweenthe hub and the shaft. However, the demand for increased storagecapacity and smaller disc drives has led to the read/write head beingplaced increasingly close to the disc surface. The close proximityrequires that the disc rotate substantially in a single plane. A slightwobble or run-out in disc rotation can cause the disc to strike theread/write head, possibly damaging the disc drive and resulting in lossof data. Further, resistance to mechanical shock and vibration is poorin the case of ball bearings, because of low damping. Because thisrotational accuracy cannot be achieved using ball bearings, disc drivescurrently utilize a spindle motor having fluid dynamic bearings on theshaft and a thrust plate to support a hub and the disc for rotation. Onealternative bearing design is a hydrodynamic bearing.

In a hydrodynamic bearing, a lubricating fluid such as gas or liquid orair provides a bearing surface between a fixed member and a rotatingmember of the disc drive. Dynamic pressure-generating grooves formed ona surface of the fixed member or the rotating member generate alocalized area of high pressure and provide a transport mechanism forfluid or air to more evenly distribute fluid pressure within the bearingand between the rotating surfaces, enabling the spindle to rotate withmore accuracy. However, hydrodynamic bearings suffer from disadvantages,including a low stiffness-to-power ratio and increased sensitivity ofthe bearing to external loads or mechanical shock events.

To increase stiffness, spindle motors have been attached to both thebase and the top cover of the disc drive housing. However, in order touse top cover attachment, the motor is open on both ends, whichincreases the risk of oil leakage. This leakage among other things iscaused by differences in net flow rate created by differing pumpinggrooves in the bearing. If the flow rates within the bearing are notcarefully balanced, a net pressure rise toward one or both ends mayforce fluid out through a seal. Balancing the flow rates is difficultbecause the flow rates created by the pumping grooves are a function ofthe gaps defined in the hydrodynamic bearing, and the gaps, in turn, area function of parts tolerances. Proper sealing is also critical. Bearingfluids give off vaporous components that could diffuse into a discchamber. This vapor can transport particles such as material abradedfrom bearings or other components. These particles can deposit on theread/write heads and the surfaces of the discs, causing damage to thediscs and the read/write heads as they pass over the discs.

Efforts have been made to address these problems. One design is atop-cover-attach conical bearing having two independent flow paths. Thisdesign uses asymmetric sealing and includes a centrifugal seal and agrooved pumping seal. Another existing design, the exclusion seal(x-seal), is used to seal interfacial spaces between the hub and shaft(shown in FIG. 4). The x-seal includes an asymmetric sealing design witha single thrust plate, wherein one end is pumped inward with thrustspiral grooves and the other end with a groove pumping seal. At thethrust bearing end, a centrifugal seal maintains oil level change in thecapillary reservoir during static to dynamic stage, and non-operatingshock. Tests have shown, however, that the centrifugal seal fails atabout 500 G shock, and oil leaks through fill holes at about 500 Gshock.

Mobile applications require higher non-operating shock than desktop orenterprise products. Laptop computers can be subjected to largemagnitudes of mechanical shock as a result of handling. It has becomeessential in the industry to require disc drives to be able to withstandsubstantial mechanical shock. A sufficient sealing system that canwithstand 1000 Gs shock is needed for mobile applications. Further, aneed exists to increase shaft stiffness and dynamic parallelism(alignment of the disc surfaces to the plane of the actuator arm motion)while simultaneously lowering bearing power.

SUMMARY

An improved sealing system is provided that withstands operating modeand non-operating mode mechanical shock for use with fluid dynamicbearings, which in turn may be incorporated into a spindle motor or thelike. In an embodiment, the sealing system withstands at least 1000 Gshock. The invention provides an asymmetric sealing method and systemand active recirculation within a hydrodynamic bearing to retain fluidand purge air.

Also provided is a system for filling the journal with fluid, whichwithstands shock. The invention further provides a method forconsumption of less power in a spindle motor, and a spindle motor thatutilizes smaller size components, yet maintains necessary stability.Also provided is a method for achieving a longer operating life for aspindle motor. Further provided is a method and system for supplyingradial stiffness within the journal. The invention additionally providesa method and system for increasing dynamic parallelism and shaft tothrust plate bond strength.

Features of the invention are achieved in part, in an embodiment, byutilizing an asymmetric sealing system. An enlarged fluid reservoir,defined between a shield and a sleeve, having a lower pressure area thanother fluid containing areas is employed. The invention utilizes a fluidrecirculation passageway in fluid communication with the enlargedreservoir to ensure the pressure due to the asymmetry in the journalbearing adjacent to the thrust plate, and inward pumping pressure fromthe thrust plate are reduced to about atmospheric pressure. Acentrifugal capillary seal is employed on an end of the reservoir. Whenthe motor is spinning, centrifugal force acts on the reservoir fluidforcing it into the bearing, and causing air to be expelled. In anembodiment, channels are included adjacent to the reservoir on a shieldallowing fluid to be retained rather than leak during a shock event. Dueto a pressure difference in the reservoir between a tight gap(non-channel portion) and a larger gap (channel portion), fluid isretained within the reservoir during shock events. The channels furtherallow air within the fluid to travel along the channel and be expelledfrom the bearing fluid. An angled fill hole is provided at an end of thereservoir for filling fluid into the bearing and also serving as alocation to expel air.

A tapered journal gap further provides asymmetric pressure as well asreduces power consumption at a journal plenum. In an embodiment, agrooved pumping seal (GPS), defined between a shield and an outerdiameter of a thrust plate, is provided. The shield is self-aligning(concentric to the hub OD) and acts as a travel limiter to the hub. Theasymmetric sealing method and system further incorporates spiralgrooves. The spiral grooves are defined on the thrust plate for activelygenerating pumping pressure to drive fluid recirculation and to pumpfluid from the thrust plate bearing toward the shaft, into the journalbearing, and beyond a journal grooving apex, when the shaft and thesleeve are in relative rotational motion. A single-sided thrust platebearing is utilized. In a further embodiment, grooved pumping isutilized within the journal for providing radial stiffness substantiallyfocused at an apex of the grooving pattern. Further, in an embodiment,an unbalanced and asymmetric grooving pattern at an end of the bearingprovides a pressure gradient and establishes a seal.

Dynamic parallelism is improved due to a larger surface contact betweenthe interface of thrush plate OD and the base. A larger thrust plateimproves the bond strength at the interface of the thrust plate andshaft.

Reduction of power consumption is achieved, in part, by utilizingsmaller size components, including a smaller diameter shaft. Stabilityof the motor is, however, maintained by attaching the shaft to the topcover. Reduction of power consumption is further achieved, in part, byemploying grooved pumping on the thrust plate OD, and utilizing athinner fluid. A larger reservoir is provided and so a thinner fluid canbe utilized, the thinner fluid typically having a higher evaporationrate than thicker fluids. The thinner fluid results in less friction andreduces power consumption by the motor. Further, in an embodiment, asingle sided thrust plate is used with magnetic preload to furtherreduce power losses in the thrust region, bearing losses occurring ononly one side of the thrust plate.

Other features and advantages of this invention will be apparent to aperson of skill in the art who studies the invention disclosure.Therefore, the scope of the invention will be better understood byreference to an example of an embodiment, given with respect to thefollowing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated by reference to thefollowing detailed description, when taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a top plan view of a disc drive data storage system in whichthe present invention is useful;

FIG. 2 is a sectional side view of a hydrodynamic bearing spindle motorillustrating features including a fluid recirculation passageway,shield, reservoir and fill hole, in accordance with an embodiment of thepresent invention;

FIG. 3 is another sectional side view of a hydrodynamic bearing spindlemotor as in FIG. 2, with FIG. 3 having a shallower cross section ascompared to FIG. 2, and the symmetric and asymmetric grooves of FIG. 2shown instead by arrows, in order to show in FIG. 3 a more detailed viewof features including a fluid recirculation passageway, shield,reservoir, fill hole, thrust plate pumping grooves, example pressures,fluid flow direction and pumping direction, and FIG. 3 not illustratingparticular features sufficiently shown in FIG. 2 including a top cover,stator winding, magnets, and baseplate, in accordance with an embodimentof the present invention;

FIG. 4 is a sectional side view of a known spindle motor design;

FIG. 5 is a perspective view of a shield sectioned to illustratechannels and an angled fill hole, in accordance with an embodiment ofthe present invention;

FIG. 6 is another perspective view of a shield illustrating channels andan angled fill hole, in accordance with an embodiment of the presentinvention; and

FIG. 7 is a sectional side view of a portion of a hydrodynamic bearingspindle motor illustrating features including a fluid recirculationpassageway, a shield attached to a thrust plate, a reservoir and a fillhole, in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION

Exemplary embodiments are described with reference to specificconfigurations. Those of ordinary skill in the art will appreciate thatvarious changes and modifications can be made while remaining within thescope of the appended claims. Additionally, well-known elements,devices, components, methods, process steps and the like may not be setforth in detail in order to avoid obscuring the invention.

A method, system and means of sealing that withstands operating mode andnon-operating mode mechanical shock for use with fluid dynamic bearingsis described herein. In an embodiment, the sealing system withstands1000 G shock by way of asymmetric sealing and pressure gradient. Asdiscussed below, in an embodiment, a fluid recirculation passageway, anenlarged fluid reservoir defined between a shield and a sleeve,reservoir channels, grooved pumping, a tapered journal gap andasymmetric journal grooves provide, in part, a system and method ofemploying an asymmetric pressure gradient. Also as discussed below, inan embodiment, the invention further utilizes the properties of agrooved pumping seal (low volume, high stiffness) and a centrifugalcapillary seal (high volume, low stiffness) in the design of the methodand system to withstand shock. Further, in an embodiment, an angledfluid fill hole avoids fluid leak during shock and is located at an endof the reservoir.

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, FIG. 1 illustrates atypical disc drive data storage device 110 in which the presentinvention is useful. Clearly, features of the discussion and claims arenot limited to this particular design, which is shown only for purposesof the example. It will be readily apparent that the present inventionmay be applied to disc drives, spindle motors, and other motors having astationary and a rotatable component. In fact, the designs discussedbelow can be used in systems where rotation between components exists,even if the components rotate in the same direction.

Disc drive 110 includes housing base 112 that is combined with cover 114to form a sealed environment. Disc drive 110 further includes disc pack116, which is mounted for rotation on a spindle motor (not shown) bydisc clamp 118. Disc pack 116 includes a plurality of individual discs,which are mounted for co-rotation about a central axis. Each discsurface has an associated head 120 (read head and write head), which ismounted to disc drive 110 for communicating with the disc surface. Inthe example shown in FIG. 1, heads 120 are supported by flexures 122,which are in turn attached to head mounting arms 124 of actuator body126. The actuator shown in FIG. 1 is a rotary moving coil actuator andincludes a voice coil motor, shown generally at 128. Voice coil motor128 rotates actuator body 126 with its attached heads 120 about pivotshaft 130 to position heads 120 over a desired data track along arcuatepath 132. This allows heads 120 to read and write magnetically encodedinformation on the surfaces of discs 116 at selected locations.

FIG. 2 is a sectional side view of a hydrodynamic bearing spindle motor255 used in disc drives 110 in which the present invention is useful.Typically, spindle motor 255 includes a stationary component and arotatable component. The stationary component includes shaft 275 that isfixed and attached to base 210. It is to be appreciated that spindlemotor 255 can employ a fixed shaft as shown in FIG. 2, or a rotatingshaft. Further, in an embodiment of the invention, shaft 275 is attachedto top cover 256, providing stability to shaft 275 and improving dynamicperformance. Thus, in a fixed shaft motor, both upper and lower ends ofshaft 275 can be fastened to base 210 and to top cover 256 of thehousing, so that the stiffness of the motor and its resistance to shockas well as its alignment to the rest of the system is enhanced.

The rotatable component includes hub 260 having one or more magnets 265attached to a periphery thereof. The magnets 265 interact with a statorwinding 270 attached to the base 210 to cause the hub 260 to rotate.Magnet 265 can be formed as a unitary, annular ring or can be formed ofa plurality of individual magnets that are spaced about the periphery ofhub 260. Magnet 265 is magnetized to form one or more magnetic poles.

The hub 260 is supported on a shaft 275 having a thrust plate 283 on oneend. Thrust plate 283 can be an integral part of the shaft 275, or itcan be a separate piece that is attached to the shaft, for example, by apress fit. Further, thrust plate 283 engages with base 210 at interface290. The invention provides an enlarged contact surface between thrustplate 283 and base 210, namely at interface 290. In an embodiment,interface 290 (the diameter of thrust plate 283 in contact with base210) is 4.5 mm. It is to be appreciated that the length of interface 290may vary, and in some cases interface 290 ranges from 3 millimeters to 5millimeters. This is achieved by an enlarged thrust plate OD contactsurface. An improvement in dynamic parallelism results, dynamicparallelism defined as the parallelism between the spinning disk andreference features in base 210 that determine a plane. A three pointdatum on base 210 is compared with the perpendicularity of the spinaxis. The invention provides an enlarged footprint, improving thedynamic parallelism of the components.

Further, due to the longer engagement between thrust plate 283 and shaft275, bond strength at the interface between thrust plate 283 and shaft275 is improved. In an embodiment, the engagement between thrust plate283 and shaft 275 is two times the engagement as compared withconventional motors (i.e., compared to the x-seal).

The shaft 275 and thrust plate 283 fit into sleeve 280 within hub 260.Hub 260 includes a disc carrier member 214, which supports disc pack 116(shown in FIG. 1) for rotation about shaft 275. Disc pack 116 is held ondisc carrier member 214 by disc clamp 118 (also shown in FIG. 1). Hub260 is interconnected with shaft 275 through hydrodynamic bearing 217for rotation about shaft 275.

A fluid, such as lubricating oil or a ferromagnetic fluid fillsinterfacial regions between shaft 275 and sleeve 280, thrust plate 283and sleeve 280, thrust plate 283 and shield 282, and between shield 282and sleeve 280. In an embodiment, angled fill hole 285 is positioned tomake a 30 degree angle (or an alternative angle, as discussed below)with a surface of shield 282. Although the present figure is describedherein with a lubricating fluid, those skilled in the art willappreciate that a lubricating gas can be used.

Typically one of shaft 275 and sleeve 280 includes sections of pressuregenerating grooves, including asymmetric grooves 240, and symmetricgrooves 244. The grooving pattern includes one of a herringbone patternand a sinusoidal pattern. As shown, asymmetric grooves 240 are placed onone end of the journal and symmetric grooves 244 are placed on anopposite end of the journal. Asymmetric grooves 240 and symmetricgrooves 244 induce fluid flow in the interfacial region and generate alocalized region of dynamic high pressure and radial stiffness. Thepressures are focused at symmetric grooves apex 246 and asymmetricgrooves apex 242. As sleeve 280 rotates, pressure is built up in each ofits grooved regions. In this way, shaft 275 easily supports hub 260 forconstant high speed rotation. In an example, the grooves are separatedby raised lands or ribs and have a small depth. In an embodiment, adiamond-like carbon (DLC) coating is utilized on shaft 275 in the regionof asymmetric grooves 240 to prevent or minimize particle generationduring any contact between shaft 275 and sleeve 280.

In addition to, or as an alternative to the pressure generating groovesas discussed in the previous paragraph, an embodiment of the inventionprovides fluid flow by other methods (as discussed in detail below). Theother methods include a tapered or widened journal area 262, anasymmetric pressure gradient, a low pressure area within reservoir 284defined between shield 282 and sleeve 280, a sleeve passageway 286, agrooved pumping seal between shield 282 and thrust plate 283, and spiralgrooves on thrust plate 283.

In an embodiment of the invention, sleeve passageway 286 is situated ata point between asymmetric grooves 240, and symmetric grooves 244.Sleeve passageway 286 is generally positioned at a midpoint along shaft275 providing a low pressure area. A low pressure area in the center ofthe motor is acceptable since a bearing in the center of the motoroffers little radial stiffness. Further, positioning sleeve passageway286 in an angled manner enables a one-piece hub to be machined.

The invention further provides a shield 282 that radially self-alignsinto sleeve 280. A light radial interference fit (light press fit) isemployed between shield 282 and sleeve 280 for self alignment. On oneend (adjacent to thrust plate 283) sleeve 280 locates shield 282radially, and on another end shield 282 is attached to hub 260 (i.e.,laser welded). The invention therefore provides, in an embodiment, aconstant gap of about 20 to 30 microns between thrust plate 283 andshield 282.

Since thrust plate 283 is single-sided, hub 260 has freedom of movementin an axial direction. Shield 282 is therefore provided by the inventionas a travel limiter to hub 260, defining a radial displacement limit tohub 260. Shield 282 also serves as a damper to hub 260 to dissipateenergy caused by mechanical shock.

FIG. 3 presents a fluid dynamic bearing system illustrating, in anembodiment of the invention, fluid pumping direction, fluid directionand example pressures. In an embodiment, an inverted shield is utilized.Shield 282 is described as inverted since capillary seal 316 is invertedas compared to an x-shield design (x-shield shown in FIG. 4). Anasymmetric pressure gradient is created by the invention. The asymmetricpressure is created by features including a fluid recirculationpassageway, an enlarged fluid reservoir defined between a shield and asleeve, reservoir channels, grooved pumping, a tapered journal gap andasymmetric journal grooves.

In an embodiment, the fluid capacity of reservoir 284 is 2.5 mg. It isto be appreciated that this capacity is not fixed. The enlarged fluidreservoir 284 having channels 510 contribute to the asymmetric pressuregradient (channels 510 shown in FIG. 5). Due to a lower flow resistanceand lower pressure in enlarged reservoir 284, compared with other fluidcontaining areas, fluid is received and retained within reservoir 284during non-operating or operating shock events. As an example, numericalexample pressures are illustrated in FIG. 3. As shown, reservoir 284shows a pressure of 0.0 psi while the journal shows pressures of 0.06psi to 135 psi. When the motor is spinning and forcing fluid bycentrifugal force from reservoir 284, pumping grooves 324 generatepumping pressure and drive fluid recirculation through the motor.However, when the motor is not spinning and centrifugal force subsides,or during shock events, reservoir 284 can receive fluid from areasincluding the outer diameter gap 346 of thrust plate 283 and from thejournal between shaft 275 and sleeve 280.

Grooved pumping is employed along the inside diameter (ID) and theoutside diameter (OD) of thrust plate 330. Pumping grooves are formed onthrust plate 283 for active recirculation. In the case of the ID, spiralpumping grooves 324 generate sufficient pumping pressure to drive fluidrecirculation and to pump fluid from thrust plate bearing passageway(adjacent to the thrust plate ID) toward shaft 275, into the journalbearing, and beyond lower journal symmetric grooving apex 246, whenshaft 275 and sleeve 280 are in relative rotational motion. Asymmetricgrooves 242 and symmetric grooves 244 also create pressure within thejournal and force fluid movement to a groove apex (as described above inFIG. 2). In an embodiment, when the motor is spinning, the fluid flowdirection is inward from the bearing of the thrust plate ID 330, alongthe journal bearing to journal plenum 312, through sleeve passageway286, to recirculation plenum 332 and then returning to the bearing ofthe thrust plate ID 330. The fluid flow direction, in an example, isillustrated by solid lines shown in FIG. 3. It is to be appreciated thatin other embodiments, the fluid flow direction may take on anotherdirection. The grooved pumping direction, in an example, is illustratedby dashed lines shown in FIG. 3. In another embodiment of the invention,thrust plate 283 is structured without pumping grooves 324.

A fluid recirculation passageway includes sleeve passageway 286 and abearing between thrust plate ID 330 and sleeve 280. Sleeve passageway286 is positioned such that one end is placed generally at a midpointalong shaft 275 and a second end joins recirculation plenum 332 suchthat, in one situation, fluid and air may travel along channels 510(FIG. 5). Recirculation plenum 332 is defined by a junction joiningreservoir 284, sleeve passageway 286, thrust plate ID 330 and thrustplate outer diameter gap 346. Sleeve passageway 286 provides a lowpressure area compared to the journal bearing. A low pressure area inthe center of the motor is feasible for the reason that a bearing in thecenter of the motor offers little radial stiffness. The lower pressurearea also advantageously reduces power consumption by journal plenum312. In an example, as shown in FIG. 3, 0.06 psi occurs at journalplenum 312, while a higher pressure occurs on either side of journalplenum 312. A wider or variable journal gap also is provided adjacent tojournal plenum 312 for creating a lower pressure area. The wider orvariable journal gap, adjacent to journal plenum 312, diverges towardjournal plenum 312.

A recirculation passageway ensures the pressure due to the asymmetry inlower journal bearing 326 adjacent to the thrust plate, and inwardpumping pressure from pumping grooves 324 of thrust plate 283 arereduced to about atmospheric pressure. The flow resistance of sleevepassageway 286 is significantly lower than the flow resistance of theupper journal 310 and lower journal 326, so a pressure drop occursacross the journal bearing.

The fluid recirculation passageway is biased for creating an asymmetricpressure gradient and substantially circulating fluid from the journalto sleeve passageway 286 and then to the bearing of thrust plate ID 330,and then returning to the journal. Capillary attraction fills thejournal area, and recirculation of the fluid purges any air within thejournal.

In an embodiment, the invention utilizes and makes use of the propertiesof a grooved pumping seal (low volume, high stiffness) and a centrifugalcapillary seal (high volume, low stiffness) to withstand mechanicalshock.

In FIG. 3, a grooved pumping seal (GPS) 318 is employed in outerdiameter gap 346 defined between shield 282 and an OD of thrust plate283. By way of pumping grooves 324, GPS 318 establishes an outerdiameter gap sealing stiffness and generates pressure substantiallyequivalent to the pressure located at recirculation plenum 332, whenshaft 275 and sleeve 280 are in relative rotational motion. GPS 318 is ahigh stiffness seal and, in an embodiment, the invention makes use ofthis characteristic by utilizing GPS 318 with an end of outer diametergap 346. GPS 318 pumps fluid from outer diameter gap 346 serving toprevent fluid leakage from fluid boundary 322. GPS 318 is a low volumeseal and the invention makes use of this characteristic. Pumping fluidfrom outer diameter gap 346 serves to reduce power consumption byestablishing air in outer diameter gap 346, thereby reducing frictionsince air is present between the OD of thrust plate 283 and shield 282.

A centrifugal capillary seal (CCS) 316 is defined between shield 282 andsleeve 280. In an embodiment, the adjacent surfaces of shield 282 andsleeve 280 have relatively tapered surfaces that converge towardrecirculation plenum 332. A meniscus is formed between the taperedsurfaces, and fluid within reservoir 284 is forced toward recirculationplenum 332 by centrifugal force when shaft 275 and sleeve 280 are inrelative rotational motion. CCS 316 is a low stiffness seal and, in anembodiment, the invention makes use of this characteristic by attachingshield 282 to hub 260 by welding or other means making a fluid barrierabove the fluid meniscus. CCS 316 is a high volume seal and theinvention makes use of this characteristic by utilizing CCS 316 with anenlarged reservoir 284.

Asymmetric sealing is also employed at upper journal 310. Asymmetricgrooves 242 generate pressure within upper journal 310 substantiallyequivalent to the pressure located at journal plenum 312. Fluid isforced from upper journal 310 generally to groove apex 242 (as describedabove in FIG. 2).

FIG. 4 illustrates an example of a fluid dynamic bearing utilizing aconventional X-seal. Motor 450 includes shaft 475, sleeve 455, path 484,thrust plate 480, shield 482, fill hole 485 and capillary seal 420. Ascan be observed, gap 425 maintains fluid (about 0.5 mg of fluid) in partby way of capillary seal 420. Further, fill hole is positioned belowcapillary seal 420. In an embodiment, the present invention utilizes anenlarged reservoir 284, channels 510, a grooved pumping seal 318 and anangled fill hole 285, thereby withstanding greater shock than the X-sealdesign, using less power and providing a longer life for the motor.Further, the present invention provides interface 290, which, in anembodiment, is a larger surface area than interface 440 of the X-sealdesign, effecting greater dynamic parallelism and shaft to thrust platebond strength.

Referring to FIG. 5, in an embodiment, reservoir 284 includes channels510. Channels 510 run in a generally axial direction along the walls ofshield 282. Channels 510 extend from recirculation plenum 332 and alongreservoir 284. In some cases, channels 510 are in-line with sleevepassageway 286. In one embodiment, six channels are employed, and inanother embodiment, two wider channels are employed. It is to beappreciated that the number, length, width and positioning of channels510 may vary and is determined by bearing requirements.

Channels 510 allow air within the fluid to travel along channels 510 andbe purged from the fluid. Channels 510 further provide a means for fluidto be retained within reservoir 284. Fluid is retained within reservoir284 during shock events due to a pressure difference between a portionof reservoir 284 having channels and a portion of reservoir 284 withoutchannels. In another embodiment of the invention, reservoir 284 servesas a low pressure area without having channels 510.

FIG. 6 illustrates an embodiment of the invention that includes angledfill hole 285. Angled fill hole 285 (or air vent hole) provides a meansto fill a fluid dynamic bearing with fluid. A predetermined amount offluid is injected into angled fill hole 285 above capillary seal 316.Angled fill hole 285 is positioned to make a 30 degree angle or analternative angle (i.e., 45 degrees) with a surface of shield 282. It isto be appreciated that angles beside 30 degree can be used. Further, inan embodiment, two angled fill holes are employed. It is to beappreciated that other numbers of angled fill holes can be utilized.Also shown in FIG. 6 is attachment location 520 wherein shield 282 isattached to sleeve 280, in an embodiment of the invention. Fill hole 285is positioned adjacent to a sealed wall at attachment location 520. Inan embodiment, fill hole 285 is positioned between channels 510. Inanother embodiment of the invention, the fill hole is positioned withoutmaking an angle with a surface of shield 282 and positioned on anothersection of shield 282.

During a shock event, fluid may travel along channels 510 and collidewith sleeve 280, decelerating the traveling fluid. Frictional drag slowsthe fluid within reservoir 284 and along channels 510, due to theviscosity of the fluid. The motion of the fluid is therefore retardedsuch that fluid may reach and collect at pool area 530 without leakingfrom fill hole 285. In some cases, pool area 530 fills with fluid slowerthan the duration of a shock event. Further, angled fill hole 285opposes escape of fluid during shock since the fluid follows a path ofleast resistance and an angled fill hole presents greater resistance incomparison to capillary force gradients.

Referring to FIG. 7, a further embodiment of the invention isillustrated. Similar to previously described embodiments, an invertedshield is employed with spindle motor 700. Also similar to previouslydescribed embodiments, enlarged reservoir 724 and sleeve passageway 726contribute to the asymmetric pressure gradient (as described above) forwithstanding shock events. Thrust plate 752 establishes an enlargedinterface 762 with base 750.

In this embodiment of the invention, however, shield 720 is attached tothrust plate 752 at shield attachment 722 and hub 754 rotates relativeto shield 720. A DLC coating is utilized on one of the relativelyrotating adjacent surfaces, namely sleeve 756 and shield 720 to preventor minimize particle generation during any contact. Further, in thisembodiment, fill hole 760 is positioned without making an angle with asurface of shield 282.

The following specific example is provided for illustrative purposes andis not intended to be limiting. Results from experiments conductedshowed, in an embodiment, the present invention utilized within aspindle motor satisfactorily withstands 1000 G shock. The shock wasdirected over six axes with pulse duration of two milliseconds, halfsine wave. In further testing, multiple shocks having the same testingconditions were directed onto a spindle motor incorporating anembodiment of the invention and the spindle motor withstood the shockevents.

Having disclosed exemplary embodiments, modifications and variations maybe made to the disclosed embodiments while remaining within the spiritand scope of the invention as defined by the appended claims. Forexample, although the present invention has been described withreference to a sealing system for a disc drive storage system and aspindle motor assembly, those skilled in the art will recognize thatfeatures of the discussion and claims may be practiced with othersystems having a stationary and a rotatable component. The componentsmay even rotate in the same direction. Further, the present invention isuseful in many additional systems requiring shock tolerance.

1-20. (canceled)
 21. An apparatus comprising: an inner component; anouter component, wherein said inner component and said outer componentdefine a journal bearing, said inner component and said outer componentare positioned for relative rotation, and said inner component and saidouter component define a portion of a stationary component and arotatable component; and a means for creating an asymmetric pressuregradient within a fluid recirculation passageway, for circulating afluid, and for purging air in said fluid, wherein said fluid circulatesabout a portion of said journal bearing, a first fluid passageway, and asecond fluid passageway, and said means for creating said asymmetricpressure gradient, for circulating said fluid, and for purging said aircomprises spiral grooves defined on at least one of a radial member andsaid outer component to generate pumping pressure to drive fluidrecirculation and to pump said fluid from said second fluid passagewaytoward said inner component and into said journal bearing, wherein saidinner component and said outer component are in relative rotationalmotion.
 22. The apparatus of claim 21 wherein: said fluid recirculationpassageway includes said first fluid passageway defined within saidouter component, said first fluid passageway is in fluid communicationwith said second fluid passageway, said second fluid passageway isdefined between said outer component and said radial member, said radialmember extends radially from said inner component, and said first fluidpassageway and said second fluid passageway are in fluid communicationwith said journal bearing at separate locations.
 23. The apparatus ofclaim 21 further comprising: a shield connected to one of saidstationary component and said rotatable component, defining a reservoirwith said outer component; and a recirculation plenum defined by ajunction joining said reservoir, said first fluid passageway and saidsecond fluid passageway.
 24. The apparatus of claim 23 furthercomprising a means for sealing said reservoir comprising a capillaryseal defined between said shield and said outer component.
 25. Theapparatus of claim 23 further comprising: axial channels on at least aportion of an inner surface of said shield extending from saidrecirculation plenum and along said reservoir, wherein said axialchannels are operable to allow air flow within said fluid to move alongsaid axial channels and be purged from said fluid.
 26. The apparatus ofclaim 21 wherein said inner component comprises a shaft and said outercomponent comprises a sleeve.
 27. The apparatus of claim 21 furthercomprising a groove pattern on a portion of one of said inner componentand said outer component comprising one of a herringbone pattern and asinusoidal pattern.
 28. A spindle motor comprising: a journal bearingdefined by an inner component and an outer component, wherein said innercomponent and said outer component are positioned for relative rotation,and said inner component and said outer component define a portion of astationary component and a rotatable component; and a means for creatingan asymmetric pressure gradient within a fluid recirculation passageway,for circulating a fluid, and for purging air in said fluid, wherein saidfluid circulates about a substantial portion of said journal bearing, afirst fluid passageway, and a second fluid passageway, said meanscomprises pumping grooves on a facing surface positioned at an outerdiameter gap defined between a shield and an outer diameter of a radialmember, and is operable to pump fluid from said outer diameter gaptoward a recirculation plenum when said inner component and said outercomponent are relatively rotating, and wherein said recirculation plenumis defined by a junction joining a reservoir, said first fluidpassageway, and said second fluid passageway.
 29. The apparatus of claim28 wherein: said fluid recirculation passageway includes said firstfluid passageway defined within said outer component, said first fluidpassageway is in fluid communication with said second fluid passageway,said second fluid passageway is defined between said outer component andsaid radial member, said radial member extends radially from said innercomponent, and said first fluid passageway and said second fluidpassageway are in fluid communication with said journal bearing atseparate locations.
 30. The apparatus of claim 28 wherein said shield isconnected to one of said stationary component and said rotatablecomponent.
 31. The apparatus of claim 28 further comprising a groovedpumping seal formed by spiral grooves on said radial member or saidshield adjacent to said outer diameter gap.
 32. The apparatus of claim28 further comprising: axial channels on at least a portion of an innersurface of said shield extending from said recirculation plenum andalong said reservoir, wherein said axial channels are operable to allowair flow within said fluid to move along said axial channels and bepurged from said fluid.
 33. The apparatus of claim 28 wherein said innercomponent comprises a shaft and said outer component comprises a sleeve.34. The apparatus of claim 28 further comprising a groove pattern on aportion of one of said inner component and said outer componentcomprising one of a herringbone pattern and a sinusoidal pattern.
 35. Amotor comprising: an inner component; an outer component, wherein saidinner component and said outer component define a journal bearing, saidinner component and said outer component are positioned for relativerotation, and said inner component and said outer component define aportion of a stationary component and a rotatable component; and a meansfor creating an asymmetric pressure gradient within a fluidrecirculation passageway, wherein said means for creating saidasymmetric pressure gradient comprises spiral grooves defined on atleast one of a radial member and said outer component operable togenerate pumping pressure to drive fluid recirculation and to pump afluid from said second fluid passageway toward said inner component andinto said journal bearing, wherein said inner component and said outercomponent are in relative rotational motion.
 36. The apparatus of claim35 wherein: said fluid recirculation passageway includes a first fluidpassageway defined within said outer component, said first fluidpassageway is in fluid communication with a second fluid passageway,said second fluid passageway is defined between said outer component andsaid radial member, said radial member extends radially from said innercomponent, and said first fluid passageway and said second fluidpassageway are in fluid communication with said journal bearing atseparate locations.
 37. The apparatus of claim 35 further comprising: ashield connected to one of said stationary component and said rotatablecomponent, defining a reservoir with said outer component; and arecirculation plenum defined by a junction joining said reservoir, afirst fluid passageway and a second fluid passageway.
 38. The apparatusof claim 37 further comprising: a means for sealing said reservoircomprising at least one of a capillary seal defined between said shieldand said outer component, and a grooved pumping seal formed by spiralgrooves on at least one of said radial member and said shield adjacentto an outer diameter gap defined between said shield and an outerdiameter of said radial member, said outer diameter gap joining saidjunction.
 39. The apparatus of claim 37 further comprising: axialchannels on at least a portion of an inner surface of said shieldextending from said recirculation plenum and along said reservoir,wherein said axial channels are operable to allow air flow within saidfluid to move along said axial channels and be purged from said fluid.40. The apparatus of claim 35 further comprising a groove pattern on aportion of one of said inner component and said outer componentcomprising one of a herringbone pattern and a sinusoidal pattern.